The present invention relates to microelectromechanical devices. Specifically, the present invention relates to latching mechanisms for microelectromechanical devices.
Relatively modern technology now enables microelectromechanical systems (MEMS) to be fabricated on semiconductor substrates, typically silicon substrates. These microelectromechanical systems typically have sizes on the order of microns and may be integrated with other electrical circuits on a common substrate. As a result, microelectromechanical systems have found their way into numerous applications across numerous disciplines. Illustrative MEMS applications include optical switching, inertial or pressure sensors, and biomedical devices, for example.
MEMS-based optical switches are used in a variety of applications for switching light waves between optical waveguides, such as fibers. Optical switches typically include a mirror coupled to one or more comb drive actuators which either moves the mirror into an optical path between optical fibers or pulls the mirror out of the optical path.
Prior devices, however, suffer numerous limitations. For instance, prior devices require power consumption in order to maintain the optical switch in a switched position. Power must be continuously supplied to the switch to avoid loss of signal. Therefore, even a brief power failure can interrupt the signal. In addition, because prior optical switches require power to maintain a switched position, they consume more power. Accordingly, there is a need for latching devices which can hold the moving parts of an optical switch in the switched position without continuous electric power.
A prior attempt to construct a latching device for a MEMS optical switch employed a permanent magnet, an iron yoke coupled to the permanent magnet, and wire coils wound around the iron yoke. The switch included a mirror mounted toward the end of a deflectable cantilever coated with gold. By applying current through the wire coils the cantilever would be magnetically drawn into contact with the iron yoke where it would remain due to the permanent magnet even after the flow of current through the coils ceased. By applying a reverse current through the coils the cantilever would be released from the yoke and return to a mechanically stable position. The device suffers from numerous drawbacks. For instance, the wire coils and yoke must be disposed in a layer outside the layer occupied by the optical paths. This increases the size of the switch and packaging complexity. Furthermore, the device is only good for bi-stable latching. That is, the device only has two stable positions, either in contact with the magnet or out of contact with the magnet.
Another attempt to construct a latching device for an optical switch used a mirror with an arrowhead-shaped tip. The device included opposed prongs for receiving the mirror tip therebetween. The opposed prongs were drawn together or pushed apart by a thermo-electric actuator. By sliding the tip of the mirror between the opposed prongs, the mirror would become secured in the switched position. To remove itself from the switched position, the thermo-electric actuator would cause the prongs to separate, thereby allowing the tip of the mirror to escape and return to its original position. This approach suffers from several drawbacks. As with the other prior art device described, the device is limited to bi-stable latching. In addition, the displacement distance of the mirror needs to be large to reach the latching position, undesirably increasing the driving power and switching time for the device. Furthermore, the thermo-electric actuator is itself a relatively slow driver, requiring on the order of 10 milliseconds to activate.
Accordingly, improvements in latching devices for MEMS-based devices such as optical switches are desired.
The present invention provides a latching device for a MEMS-based system, such as an optical switch. In accordance with one embodiment of the invention, a micro electromechanical system is formed on a substrate. The system includes a positionable member capable of being moved between at least two positions relative to the substrate. An actuator such as a comb drive actuator is provided which may include a stationary comb mounted on the substrate, a moveable comb interleaved with the stationary comb, and a beam connected between the substrate and the moveable comb. The actuator is coupled to a latching member so that the latching member can be moved between a first position and a second position. In the first position, the latching member engages the positionable member to prevent the positionable member from moving. In the second position, the latching member is disengaged from the positionable member to allow movement of the positionable member. The combs of the comb drive actuator deflect the beam to move the latching member from the first to the second position.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.